function show_default_values(){
    form_ids = ["form_bkpj"]
        
    for (var i=0; i<form_ids.length; i++){
        elem_form = document.getElementById(form_ids[i])
        elem_list = elem_form.getElementsByTagName('input')
            
        for (var i=0; i<elem_list.length; i++){
            if (elem_list[i].type == 'range'){
                show_value(elem_list[i])
            }
        }
    }
}


// show the value of <input type='range'> at the <span> before it
function show_value(elem){
    elem.previousElementSibling.innerHTML = elem.value
}


// AJAX 发送参数值
function submit_form(elem_submit){
    elem_form = elem_submit.parentElement
    
    xhr = new XMLHttpRequest();
    xhr.open("POST", elem_form.action);
    xhr.send(new FormData(elem_form));

}

